The present invention relates to collimators in radiation therapy devices, and more particularly to multiple layer multileaf collimator design to improve resolution and reduce leakage.
During conventional radiation therapy treatment, a beam of radiation, varying in angles and intensities, is directed at an area of a patient, e.g., at a tumor. Typical treatment field shapes, square, rectangular, or a modification thereof, result in a three-dimensional treatment volume that, unfortunately, may include healthy tissue and organs. For obvious safety reasons, the dose capable of being delivered to the tumor is limited by the healthy tissue and organs in the path of the radiation beam. Since cure rates for many tumors are a sensitive function of the dose they receive, reducing the amount of exposed healthy tissue and organs is highly desirable in order to be able to increase the dose delivered to the tumor. Methods of making the treatment volume correspond more closely with a tumor include moving solid-jaw blocks during treatment, scanning the radiation beam over the volume to be treated, and using a multileaf collimator to create an irregularly shaped field related to the shape of the tumor.
An example of a multileaf collimator arrangement positioned about the central axis of a radiation-emitting head for shaping an irradiated beam is disclosed in U.S. Pat. No. 5,166,531, issued to Hunzinger on Nov. 24, 1992. Two opposing arrays of side-by-side elongated radiation blocking collimator leaves act in place of opposing solid jaw blocks. Each leaf in each opposing array can be moved longitudinally towards or away from the central axis of the beam, thus defining a desired shape through which the radiation beam will pass.
An enhancement on the multileaf collimator approach is described in U.S. Pat. No. 5,591,983, issued to Yao on Jan. 7, 1997. In Yao, a multiple layer multileaf collimator design is formed through first and second layers of a plurality of elongated radiation blocking leaves. The leaves of each layer are arranged adjacent one another so as to form two opposed rows of adjacently positioned leaves and are movable in a longitudinal direction which can be either generally transverse to or in the same direction of the beam. The layers are arranged one above another in the beam direction and offset in a lateral direction, so that spaces between adjacent leaves of the first and second layers are positioned over and under, respectively, leaves of the respective first and second layers. The arrangement of the leaves allows a reduction in problems of radiation leakage between leaves of a multileaf collimator. However, the arrangement does not provide as fine a resolution as desired to allow more accurate block positioning for creating a block volume in correspondence with a tumor shape.
Accordingly, what is needed is a system and method for utilizing a multiple layer multileaf collimator arrangement that improves resolution and reduces leakage for radiation delivery. The present invention addresses such a need.
The present invention provides aspects of a multiple layer multileaf collimator capable of improving resolution for coverage of a target during radiation therapy. A multiple layer multileaf collimator includes a first layer of multiple elongated radiation blocking leaves supported by a first frame for individual leaf positioning in a first direction. The multiple layer multileaf collimator further includes a second layer of multiple elongated radiation blocking leaves supported by a second frame for individual leaf positioning in a second direction, the second direction offset at a desired angle relative to the first direction, wherein the individual leaves of the first and second layers conform more closely with a target shape to improve resolution. Further, in a preferred aspect, the second layer is positioned above the first layer and provides leakage coverage for the multiple elongated radiation blocking leaves of the first layer.
Through the present invention, more precision in blocking radiation from healthy tissue and organs during radiation therapy is achieved. Such benefits are particularly significant to provide more effective treatment in the elimination of unhealthy target areas. Thus, the present invention allows one to increase the dose delivered while not exceeding healthy tissue constraints. These and other advantages of the aspects of the present invention will be more fully understood in conjunction with the following detailed description and accompanying drawings.